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- 24 Volt, 2 Amp Bench Top Power Supply 

Make] Projects 

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build, hack, tweak, share, discover,- 

0-24 Volt, 2 Amp Bench Top 

Power Supply 

Written By: Colombo 


Breadboard 3"x5"(1) 

Jameco Part no. 616690 - trim to fit 


Jameco Part no. 23579 NOTE: LM317's in a TO-220 case are 1.5 amp max!!) 

Heats ink TO-220 (1) 
Jameco Part no. 326596 

Bridge rectifier (1) 
Jameco Part no. 178183 

120 VAC to 24 VDC transformer (mine is part number LP-575^ (1) 
Jameco Part no. 1 12513 

Power Cable (1) 

Jameco Part no. 124434 or similar 

Electrolytic Capacitor IQOOuF (2) 
Jameco part no. 609553 

Capacitors: 0.1 F(1) 
Jameco Part no. 15272 

• Capacitor: 1uf (1) 
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- 24 Volt, 2 Amp Bench Top Power Supply 

Jameco Part no. 544956 

100 ohm 1/4W 5% resistor (brown black brown gold) (1) 
Jameco Part no. 691340 buys you 100 of them 

5k Linear Potentiomater (1) 
Jameco Part no. 286265 

Diode: 1N4002(1) 

Jameco Part no. 76961 buys 10 ea. 

Knob- Plastic 1/4" shaft (1) 

Jameco Part no. 265069 is shown, but Jameco has over a dozen that will work fine - 

look for 1/4" shaft to match your variable resistor, and pick one that you like the look of! 

Mini Volt Meter (ID: 460 from Adafruit Industries NOTE: These operate from +3.2V to 
+30V DC and are powered by the supply being measured) (1) 

24"x24" piece of 1/2" plywood (1) 


1/2" long x 1/8" wide nuts and bolts (8) 

half inch wood screws (6) 






Hobbyist electronics projects need robust, reliable power supplies for prototyping and 
testing. I learned how to build this circuit from the Basic Analog Circuits class at ITP taught 
by Eric Rosenthal, but took it several steps further in building a solid enclosure and 
integrating a voltage meter. Now it lives on my desk, ready to power most small projects I'm 
working on. 

You'll see example shots of point-to-point wiring of components to perfboard while following 
a schematic for this power supply. A wood enclosure is built, and Adafruit's Mini Volt Meter, 
V out posts, and a potentiometer are mounted in the final product. 

Parts List: 

© Make Projects Page 2 of 8 

- 24 Volt, 2 Amp Bench Top Power Supply 

One 3x5" perfboard 

LM31 7 variable voltage regulator 

BR805D Bridge Rectifier 

Heat Sink 

120 VAC to 24 VDC transformer (mine is part number LP-575) 

Power cable 

Two 1000 microfarad capacitors 

One 0.1 microfarad capacitor 

One 1 microfarad capacitor 

One 100 ohm resistor 

One 5k ohm variable resistor 

One 1N4002 diode 

1/2" plywood 

1/8" wood or MDF 

six half inch wood screws 

8 1/2" long x 1/8" wide nuts and bolts 

Plastic knob 

Mini volt meter from Adafruit Industries 

© Make Projects Page 3 of 8 

- 24 Volt, 2 Amp Bench Top Power Supply 

Step 1 — 0-24 Volt, 2 Amp Bench Top Power Supply 

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• Solder the positive and negative (red and black) leads from the transformer to the power 
cable. Twist the threaded wires together and use a liberal amount of solder, completely 
covering all connections. Finish with heat shrink tubing or electrical tape. 

• Apply thermal compound to LM317 and screw into heat sink. 

• Wire all components to the perfboard. There are a couple of ways to go about this: some 
find it's easier to put all the components into the holes first and bend the wires so they stay 
in place, then solder everything together. I like to go step by step, following each part of 
the schematic individually to verify that I have every connection correct. 

• You'll be using point-to-point wiring on the back of the perfboard. Make sure that all your 
connections are separated, and use insulated wires if you have to cross over any 
connections you've already made. 

• Make sure to solder leads onto your potentiometer for easy mounting to the enclosure later 
on. Also be sure to short out the middle pin to an adjacent pin on the pot, so it functions as 
a variable resistor and not a voltage divider. 

• Solder long leads to two header pins on your positive and negative output for easy 
mounting to the enclosure later on. 

© Make Projects 

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- 24 Volt, 2 Amp Bench Top Power Supply 

Step 2 


• Solder the mini volt meter directly 
to the output leads. 

• Now you should be ready to 
test your power supply. 
Remember that you are working 
with high voltage from the mains. 
Use all proper precautions when 
testing, and if you don't know what 
those are, find someone who does 
and can help you! 

• Be ready to unplug quickly if you 
see smoke or smell something 
funny. Usually this might happen 
because a component is shorted 
and burned out. It can generally be 
diagnosed and fixed relatively 

© Make Projects 

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- 24 Volt, 2 Amp Bench Top Power Supply 

Step 3 

• There are many different ways to build wooden boxes for project enclosures. Briefly, I 
used the thick plywood as a base to drill into, and attached the thinner sidewalls with 
machine screws after drilling pilot holes. I then hot-glued the sides and top together. 

• I used a 1" hole saw to snake the power cable through. This leaves room for the plug to fit 
through and also aids in ventilation. 

• Attach the perfboard and transformer to the bottom of the enclosure using nuts and bolts. 

© Make Projects 

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- 24 Volt, 2 Amp Bench Top Power Supply 

Step 4 

• Drill holes for your potentiometer and power terminals, and cut a space for your volt meter. 
I used a laser cutter to do this step, but it can also be done with a drill and a coping saw or 
scroll saw. 

• Twist the positive and negative leads to two separate screws. These will serve as your 
power terminals. 

• Attach power terminals and potentiometer to the face of the enclosure using nuts. 

• The mini volt meter comes with mounting holes, but I opted to hot glue it into place. This 
seemed to secure it well. 

© Make Projects 

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- 24 Volt, 2 Amp Bench Top Power Supply 

Step 5 

• Carefully tuck all your wires into the enclosure and hot glue the control panel to the rest of 
the enclosure. 

• Attach a knob to your potentiometer. 

• Make sure you've clearly labelled your positive and negative terminals. Now you can 
easily attach alligator clips to them and use this adjustable power supply for many different 
types of electronics projects. 

This document was last generated on 201 2-1 1 -23 06:46:09 AM. 

© Make Projects 

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